Typical building safety alarm systems may include a plurality of detectors distributed throughout a building. Upon detecting an alarm condition, signals from one or more of these detectors may be sent to notification appliances which may emit audible alarms and/or flashing lights to alert occupants of the detected condition. The audible alarm may be in the form of a page, alert tones, recorded message, etc, and may be generated by a sound generation device, e.g. a piezoelectric sound device, an electromagnetic sound device, etc. In some applications, it may be important that the sound be at a pressure level that it may be heard over ambient noise. For example, NFPA 72 “National Fire Alarm Code” has required that speakers used in fire systems produce a sound that is at least 15 dB above the noise of a given area.
Notification appliances that are located on the exterior of buildings or in hazardous environments may encounter more demanding conditions of operation. Generally, such a notification appliance may include a housing which may house an audible sound generation device, such as a horn or speaker system, and a strobe light. The housing may generally protect the sound generation device and related electronics from the environment (rain, snow, dust, etc.). The housing may further include a plurality of openings in the form of a grill located adjacent the sound generation device for allowing the sound of the audible alarm to exit the appliance.
In some configurations, the shape and design of the grill may allow rain and snow to enter the interior of the enclosure and cause less than optimum performance (freezing, reduced audible output, failure of electronics, etc.). A rain test specification for such weather proof appliances, CAN/ULC-S525-07, section 7.18.6.A, has been developed to test whether rain will unduly degrade functional performance. In general, the test specification of CAN/ULC-S525-07 involves the spraying of water on such notification appliances at a 45° angle for a period of time, and requires that the sound pressure level shall not be reduced by more than 3 dB after the water spray application compared to the value before the water spray application when measured at the same distance.